Intradermal injections are used for delivering a variety of substances. Many of these substances have proven to be more effectively absorbed into or react with the immune response system of the body when injected intradermally. Recently, clinical trials have shown that hepatitis B vaccines administered intradermally are more immunogenic if administered intramuscularly. In addition, substances have been injected intradermally for diagnostic testing, such as, for example using what is known in the art as the “Mantoux test” to determine the immunity status of the animal against tuberculosis and the immediate hypersensitivity status of Type I allergic diseases.
An intradermal injection is made by delivering the substance into the epidermis and upper layers of the dermis. Below the dermis layer is subcutaneous tissue (also sometimes referred to as the hypodermis layer) and muscle tissue, in that order. There is considerable variation in the skin thickness both between individuals and within the same individual at different sites of the body. Generally, the outer skin layer, epidermis, has a thickness between 50–200 microns, and the dermis, the inner and thicker layer of the skin, has a thickness between 1.5–3.5 mm. Therefore, a needle cannula that penetrates the skin deeper than about 3.0 mm has a potential of passing through the dermis layer of the skin and making the injection into the subcutaneous region, which may result in an insufficient immune response, especially where the substance to be delivered intradermally has not been indicated for subcutaneous injection. Also, the needle cannula may penetrate the skin at too shallow a depth to deliver the substance and result in what is commonly known in the art as a “wet injection” because of reflux of the substance from the injection site.
The standard procedure for making an intradermal injection is known to be difficult to perform, and therefore dependent upon experience and technique of the healthcare worker. This procedure is recommended to be performed by stretching the skin, orienting the bevel of a 26 Gauge short bevel needle cannula upwardly and inserting the needle cannula to deliver a volume of 0.5 ml or less of the substance into the skin of an animal with the needle cannula being inserted into the skin at an angle varying from around 10–15 degrees relative to the plane of the skin to form a blister or wheal in which the substance is deposited or otherwise contained. Accordingly, the technique utilized to perform the standard intradermal injection is difficult and requires the attention of a trained nurse or medical doctor. This procedure also makes it essentially impossible to self-administer an intradermal injection. Inserting the needle to a depth greater than about 3.0 mm typically results in a failed intradermal injection because the substance being expelled through the cannula will be injected into the subcutaneous tissue of the animal. Further, the standard method is not suitable for self-administration of intradermal injections.
Further, with the advent of viral infections that are transferred through contact with bodily fluids, it is desirable to enclose or conceal a needle cannula subsequent to administering an injection. Preferably, a delivery device should include a mechanism that is capable of enclosing a needle cannula immediately subsequent to administering the injection. If a needle is left uncovered for even a short period of time after administering an injection, such as, for example, while trying to reattach a needle cap, a biohazard exists. Therefore, it is desirable to provide an intradermal delivery device with a means for enclosing the needle cannula that is simply designed, easy to use, and readily available immediately after administering an injection.
Accordingly, there has been a need for a delivery device providing the ability of performing an intradermal injection of substances which overcomes the problems and limitations associated with conventional devices which may also be self-administered. Further, there has been a need to provide the delivery device with the ability to enclose a needle cannula immediately subsequent to administering the intradermal injection. The combination of these two features in the same delivery device would provide the ability to both reduce the probability of error and pain caused from the intradermal injection and to conceal the needle cannula after the injection has been administered.